Evaluating the performance of mechanisms for propelling a vehicle through a fluid involves determining propulsive efficiency. Propulsive efficiency η may be defined as the ratio of the rate of work {dot over (W)} done by the propulsion system over mechanical power used for propulsion, or mechanical propulsive power P. That is, propulsive efficiency may be defined as η≡{dot over (W)}/P.
One known technique of measuring propulsive efficiency involves placing sensors on a propulsor (such as a propeller) of the vehicle to measure the rate of work and mechanical propulsive power. Another known technique infers propulsive efficiency from the performance of the vehicle, such as the acceleration after a sudden power increase in the propulsion system. Another known technique estimates propulsive efficiency from the kinematics of an object traveling in the wake of the vehicle. Another known technique infers propulsive efficiency from the muscle power or metabolic rate associated with the propulsion.
These known techniques, however, are not satisfactory in certain situations. For example, known techniques may require complex equipment for measuring propeller propulsion. It is generally desirable to have satisfactory techniques in these certain situations.